The radio interphone is a professional wireless communication tool in the mobile communication, and is also a consumer tool with characteristics of the consumer product which can satisfy the requirements of user's daily life. Due to its instant communication, economy and practicality, lower cost, convenient usage and no communication fee, the radio interphone is widely used in various fields, such as civil field, military field and emergency process. In terms of design technique, the radio interphone can be classified into an analogy interphone that is designed by the analogy communication technique (which is also referred to a conventional interphone) and a digital interphone that is designed by the digital communication technique. The analogy interphone modulates the stored signal onto the transmission frequency of the interphone. The digital interphone digitalizes the voice signal to transmit the signal in the form of digital code, that is to say, all modulated signals transmitting on the transmission frequency of the interphone are digital.
To improve the communication range and capability of various interphones, such as a handset, a vehicle-mounted set and a fixed station, in the communication system and improve a coverage radius of the system, a conventional digital mobile radio (DMR) relay system is generally adopted. In this system, by means of a repeater transeriver, the received signal in a certain band is forwarded in other frequency by the transmitter thereof directly. The two signals of different frequencies have no influence on each other, or two customers are allowed to communicate on different frequencies respectively.
In the conventional DMR relay system, the interphone is required to transmit the signal in the predetermined power; but in some application scenes, to ensure the reliability of the communication, relatively higher transmission power needs to be provided. For example, for a DMR handset used in a market to communicate with a headquarter further away, higher transmission power is needed when the customer goes into an elevator. However, due to the action in the market, the moving distance of the handset in the market is small. Since the handset is very close to the repeater transeiver in most cases, the communication can be implemented in the lower power. In this case, the transmission with the higher power will shorten the service life of the battery, and can also increase the adjacent channel interference and generate stronger radiation.